The present invention relates to a process of producing a butadiene polymer. More particularly, the present invention relates to a process of producing 1,2-polybutadiene containing 70% or more of the 1,2-structure, and having a regulated melting point.
It is well-known that syndiotactic 1,2-polybutadiene having a relatively high melting point can be produced by polymerizing 1,3-butadiene in the presence of a catalyst which has been prepared from a solvent soluble cobalt compound and an organoaluminium compound. However, this known process has not yet been successfully utilized in industrial work, because of its disadvantages of low yield and unsatisfactory physical properties of the resultant polymer.
In order to overcome the above-mentioned disadvantages, a new type of catalyst comprising a cobalt compound, an organoaluminium compound and carbon disulfide was described and claimed in British Patent No. 1310621. This type of catalyst can convert 1,3-butadiene in an inert organic solvent to syndiotactic 1,2-polybutadiene having a relatively high melting point of approximately 200.degree. to 215.degree. C. and a high crystallinity. However, this type of catalyst is disadvantageous for industrial production of 1,2-polybutadiene because of the relatively low yield thereof and the difficulty in controlling the melting point of the resultant polymer. In order to eliminate the above-mentioned disadvantages, a still new type of catalyst comprising a cobalt compound, an organoaluminium, carbon disulfide and a nitrile compound was provided. One problem in this catalyst is that the nitrile compound, which is harmful to the human body, is difficult to recover from the polymerization mixture in which the catalyst is contained.